Fluteless thread-forming tools



April 27, 1965 s. s. KAHN 3,180,202

FLUTELESS THREAD-FORMING TOOLS Filed May 28, 1963 3 Sheets-Sheet 1 FIG 1gllf .25; Bllb 33 Bl/a 34 I I [4W2 l4 2 0 4. 14w! l4y y INVENTOR.

SIMON S. KAHN A ril 27, 1965 s. s. KAHN FLUTELESS THREAD-FORMING TOOLS 3Sheets-Sheet 2 Filed May 28, 1963 INVENTOR.

SIMON s. KAHN ATTYS.

3,180,202 FLUTELESS AD-FGRMING TOGLS Simon S. Kahn, Glen Ridge, N.J.,assignor to General American Transportation Corporation, Chicago, Ill.,a corporation of New York Filed May 28, 1963, Ser. No. 283,835 13Claims. (Cl. 85- 26) The present invention relates to fiutelessthread-forming tools, and more particularly to such tools adapted toswage threads of desired formation in generally cylindrical surfaces.

A general object of the invention is to provide a flutelessthread-forming tool that comprises an elongated shank including agenerally cylindrical rear body portion and a generally frusto-conicalforwardly-tapered front pilot end portion, and a continuous threadcarried on the shank and including both a plurality of helical turns onthe rear body portion and a plurality of helical turns on the frontpilot end portion, the thread having a fixed pitch, the turns on therear body portion having substantially the same minor radius and thesuccessively forward ones of the turns on the front pilot end portionhaving gradually reduced minor radii, the turns on at least one of theshank portions having a crest projection from the root thereof that iscyclically variable between maximum and minimum values along the helixof the thread with a rotational angle A about the longitudinal axis ofthe shank between adjacent thread positions of maximum crest projection,wherein A=360+B, and wherein B is a fixed angle within the approximaterange 60 to 120.

Another object of the invention is to provide a fluteless thread-formingtool of the character described, wherein the turns on the front pilotend portion have a crest projection from the root thereof that issubstantially fixed, and wherein it is the turns on the rear bodyportion that have the cyclically variable crest projection from the rootthereof, as described above.

Another object of the invention is to provide a fluteless thread-formingtool of the character described, wherein the turns on the rear bodyportion have a crest projection from the root thereof that issubstantially fixed, and wherein it is the turns on the front pilot endportion that have the cylically variable crest projection from the rootthereof, as described above.

Another object of the invention is to provide a fluteless thread-formingtool of the character described, where both the turns on the front pilotend portion and the turns on the rear body portion have the cyclicallyvariable crest projection from the root thereof, as described above.

A further object of the invention is to provide a flutelessthread-forming tool of thecharacter described, that is in the form of athread-swaging and fastening screw, and that includes an enlargedtool-engaging head on the rear end of the shank thereof, whereby thescrew swages a thread in a preformed opening provided in an associatedworkpiece, as the screw is set in the workpiece.

Further features of the invention pertain to the particular arrangementof the elements of the fluteless threadforming tool; whereby theabove-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following specification, taken inconnection with the accompanying drawings, in which:

FIGURE 1 is a combination side view of a blank and a plan view of arolling die that are employed in making the fiuteless thread-formingtool embodying the present invention; 7

FIG. 2 is a side elevational view of one form of the nited States Patent"ice tool embodying the present invention and that is in the form of athread-swaging and fastening screw;

FIG. 3 is an enlarged fragmentary side elevational view of the frontpilot end portion and the adjacent rear body portion of the shank of thescrew of FIG. 2;

FIG. 4 is an enlarged lateral sectional view of the screw, this viewbeing taken in the direction of the arrows along the line 4-4 in FIG. 3;

FIGS. 5, 6 and 7 are three diagrammatic illustrations of the variablemajor radius of the thread provided on the rear body portion of thescrew, as shown in FIGS. 3 and 4;

FIG. 8 is an enlarged fragmentary vertical sectional view of a workpiecehaving a generally cylindrical opening therethrough;

FIG. 9 is an enlarged fragmentary Vertical sectional view of theworkpiece of FIG. 8, illustrating the thread formation that is swaged inthe cylindrical opening provided therein by the utilization of the screwof FIGS. 2 to 4, inclusive;

P16. 10 is a side view of a modified form of blank that may be employedin making another form of the screw embodying the present invention;

FIG. 11 is a side elevational view of the other form of the screw thatmay be produced from the blank of FIG. 10; and

FIG. 12 is a side elevational view of a further form of the screwembodying the present invention that may be produced from the blank ofFIG. 10.

Referring now to FIGS. 2 to 4, inclusive, of the drawings, there isillustrated a fiuteless thread-forming tool, in the form of acombination thread-swaging and fastening screw 19, and embodying thefeatures of the present invention, and that may be made in accordancewith the present method; which screw 10 comprises an elongated shank 11including a forwardly tapered substantially frusto-conical front pilotend portion 11a and a substantially cylindrical rear body portion 11b.Also, the screw it comprises an enlarged head 12 terminating the extremerear end of the rear body portion 11b of the shank 11; which head 12 maybe of any suitable type, a pan head 12 being illustrated for the purposeof the present description. The head 12 carries a cross-slot 13 that isadapted to receive the bit of a screw driver, or the like, not shown,that is employed to set the screw 10. Further, the screw 10 comprises acontinuous rolled thread 14 carried on the shank 11 and including anumber of front helical turns 14a and 14b disposed on the front pilotend portion 1 1a and a number or" rear helical turns 14w1, 14x1, 14y1,142,1, 14w2, 14x2, 14 2, 1422, etc., disposed on the rear body portion1117.

Referring now to FIGS. 3 and 4, it will be observed that the thread 14has a fixed pitch; the front turns 14a and 1412 have a progressivelyincreasing minor diameter and a progressively increasing major diameterin the rear ward direction along the front pilot end portion 11a; andthe rear turns llwl, 14x1, etc., 14w2, 14x2, etc., have a fixed minordiameter and a cyclically variable major diameter in the rearwarddirection along the rear body portion 11b. Specifically, the minorradius of the rear turns 14w1, etc., is R0, while the major radius ofthe rear turns 14w1, etc., varies between the values R1 and R5, throughthe values R2, R3 and R4. Also, the maximum major radius of the rearturns 14w etc., is referred to as R and the minimum major radius of therear turns 14w1, etc., is referred to as r.

Referring now to FIGS. 5, 6 and 7, the three lines A0, B0, and C0 arerespectively arranged in mutually intersecting relation at the center 0and are respectively dis posed from each other; and the circles R1, R2,R3, R4- and R5 are respectively arranged in concentric rela-' tion toeach other about the center 0. In FIG. 5: the

curve 14-1 proceeds from the line A through 240 to the line COdecreasing gradually from the radius R to the radius R1 in the generalmanner of a spiral of Archimedes; and the curve 14-2- proceeds from theline CO through 240 to the line BO increasing gradually from the radiusR1 to the radius R5 in the general manner of a spiral of Archimedes. inFIG. 6: the curve 14-3 proceeds from the line BO through 240 to the lineA0 decreasing gradually from the radius R5 to the radius R1 in thegeneral manner of a spiral of Archimedes; and the curve 14-4 proceedsfrom the line AO through 240 to the line CO increasing gradually fromthe radius R1 to the radius R5 in the general manner of a spiral ofArchimedes. In FIG. 7: the curve 14-5 proceeds from the line CO through240 to the line BO decreasing gradually from the radius R5 to the radiusR1 in the general manner of a spiral of Archimedes; and the curve 14-6proceeds from the line BO through 240 to the line A0 increasinggradually from the radius R1 to the radius R5 in the general manner of aspiral of Archimedes. The curves 14-1, 14-2, 14-3, 14-4, 14-5 and 14-6of FIGS. 5, 6 and 7 represent five of the rear turns of the thread 14provided upon the rear body portion 11b of the shank 11 of the screw 10,as shown in FIG. 3. Thus, it will be observed: the major radius of thetop of the rear, turn 14w1 is equal to R5, as shown at the beginning ofthe curve 14-1 on the line A0 in FIG. 5; the major radius of the top ofthe rear turn 14x1 is equal to R3, as shown at the intersection of thecurve 14-2 with the line A0 in FIG. 5; the

major radius of the top of the rear turn 143 1 is equal to R1, as shownat the intersection of the curve 14-3 with the line A0 in FIG. 6; themajor radius of the top of the rear turn 14z1 is equal to R3, as shownat shown at the intersection of the curve 14-5 with the line A0 in FIG.7; and the major radius of the top of the rear turn 14w2 is equal to R5,as shown at the end of the curve 14-6 on the line A0 in FIG. 7.Accordingly, it will be understood: the thread 14 proceeds cyclically,from the maximum major radius R5 to the minmum major radius R1, throughthe angle of 240, and then from the minimum major radius R1 to themaximum major radius R5, through the angle of .240"; between twoadjacent positions of the maximum major radius R5, there is disposed anangle of 480; and between two adjacent positions of the maximum majorradius R5 in the same line A0, B0 or CO, there is disposed an angle of1440. This angle of l440 corresponds to 4 complete turns of the thread14; whereby it will be observed that there are 3 complete turns of thethread 14 between the two adjacent positions of the maximum major radiusR5 in the line A0,.as illustrated in FIGS. 5, 6 and 7. Generalizing uponthis angle of 480", in the form of the thread 14 illustrated, the samemay be designated A, where A=360+B, where B -l20f.

Considering now the general mode of operation of the screw 10, it isfirst noted that the same isespecially adapted for use in threading agenerally cylindrical sur: face. For example, as shown in FIG. 8, theworkpiece 269 has a generally cylindrical hole or bore 21 formedtherein; and it may be assumed that the cylindrical surface of this bore21 is to be threaded, as indicated at 21a in FIG. 9, employing the screw10. In this case, the pilot end 1141 of the shank 11 of the screw 1% isinserted into the bore 21; and the screw 10 is pressed toward theworkpiece and rotated, employing a screwdriver, or the like. As theshank 11 is thus rotated, the two front helical turns 14a and 145provided upon the front pilot end portion 11a break the cylindricalsurface of the bore 21 and swage the metal of the workpiece 20 to beginthe internal thread formation 21a. The rear threads 141121, 14x1, 14 1,ldzl, etc., successively enter and swage the metal in the bore 21, so asto produce the internal thread formation 21a, without the production ofchips, and entirely by the swaging action of the thread 14 upon thesurface of the bore 21.

In connection with FIGS. 8 and 9, it will be appreciated that the thread21a has a minor diameter that is smaller than the initial diameter ofthe bore 21 and a major diameter that is larger than the initialdiameter of the bore 21. In other words, in the swaging action of thethread 14 upon the bore 21, the metal of the workpiece 20 is movedradially inwardly to form the root of the thread 210, and the metal ofthe workpiece 20 is moved radially outwardly to form the crest of thethread 21a, which movements of the metal mentioned is caused by thepeculiar eccentricity of the rear turns 14-w1, 14x1, 143 1, 1421, 14w2,etc., provided upon the rear body portion 11b of the shank 11.Specifically, the thread formation 21a in the workpiece 20 has the minordiameter 2(R0) and the major diameter 2(R5), as illustrated in FIG. 9.

' Turning now to the present method of making the screw it), acorresponding blank B10 is provided, as illustrated in FIG. 1. The blankB16? is forged or formed of metal and comprises an elongated shank B11including .a subtrated at 30 in FIG. 1.

stantially frusto-conical front pilot end portion Ella and asubstantially cylindrical rear body portion B1112. Also, the blank B10comprises the pan head B12 terminating the rear end of the rear bodyportion 13111). Also, there are provided a pair of rolling dies, one ofwhich is illus- The die 30 illustrated comprises a main body portion 31and a corner card portion 32. The top of the main body portion 31 isdisposed in a given reference plane, while the top of the corner cardportion 32 is disposed above the given reference plane mentioned.Specifically, the top of the corner card portion 32 is sloped upwardlyout of the reference plane both from left to right and from top tobottom, as shown in FIG. 1. Further, in the top of the die 30 alternatelands 33 and flutes I 34 are arranged in parallel skewed relation inorder to define the complement of the thread 14 provided upon the shank11 of the screw. Of course, two complementary rolling dies are provided,although only one of these dies 30 is illustrated in FIG. 1. The shankB11 of the blank B19 is subjected to rolling pressure between thecomplementary mating fiat dies described; whereby the continuous thread14 is formed upon the shank 11 of the resulting screw 10.

Ordinarily, the metal blank B10 is formed of low carbon steel; and afterthe screw 10 is formed therefrom in the present rolling method, the sameis subjected to heat treatment so as to case harden it, in a well-knownmanner. Specifically, it is highly desirable that the front helicalturns 14:: and 14b, as well as the rear helical turns 1411 1, 14x1,14y1, 1421, 141x 2, 14x2, 143 2, 14z2, etc., be quite hard, since thescrew It is frequently employed in forming an internal thread 21a in thepilot hole 21 provided in the workpiece 20, when such workpiece Ztl isformed of steel.

Again referring to FIGS. 3 to 7, inclusive, the sections of the thread14 providedupon the rear body portion 11b of the shank 11 that have themajor radius R5 may be viewed or considered as lobes, provided thereon,since all other sections of the thread 14 have a major radius that isless than R5, and in the range from R5 down to R1. In this illustratedformation or embodiment of the thread 14 there is an angle of 480between adjacent lobes along the thread 14. Accordingly, there are threelongitudinaly extending rows of the lobes along the thread 14, as viewedfrom the front of the screw it), as illustrated in FIG. 4; which threerowsare angularly spaced-apart by 120 about the longitudinal center lineof the shank 11. This is the case, where B=120 in the general formula:A=360 +B, as previously explained.

Now in this formula, the angle B may have any desired value in theapproximate range 60 to 120. When the angle B has a value (60, 72 orthat is evenly divisible into 360, the lobes in the thread 14 aredisposed in straight rows extending longitudinally along the rear shankportion 11b; and when the angle B has a value that is not evenlydivisible into 360, the

lobes in the thread 14 are disposed in skewed rows extendinglongitudinally along the rear shank portion 1b. In these severalembodiment of the thread 14: when the angle B is 60, there are 6longitudinally extending rows of lobes; when the angle B is 72, thereare 5 longitudinally extending rows of lobes; when the angle B is 80,there are 9 longitudinally extending rows of lobes; when the angle B is90, there are 4 longitudinally extending rows of lobes; and when theangle B is 120, there are 3 longitudinally extending rows of lobes. Ineach case, the rows of lobes are equally spaced-apart about thelongitudinal center line of the shank 11. While a wide variety of thesethread formations are entirely satisfactory, it has been found thatthose designs involving an odd number of rows of lobes are generallypreferred, since these thread formations are easy to drive and provide abetter balance of the torque required in the starting of the reareccentric portion of the thread 14 into the pilot hole 21 in theworkpiece 2a in setting the screw 10, in the manner previouslyexplained.

Referring now to FIG. 10, a modified form of blank B119 is thereillustrated that is essentially the same as the blank B11) of FIG. 1,except the enlarged head B112 thereof is or hexagon form and is thusadapted to cooperate With a socket-Wrench, or the like, instead of ascrewdriver. Also, the front pilot end portion 13111:: of the shank B111is somewhat elongated by virtue of the circumstance that it is adaptedto carry several front helical turns of the thread, as explained morefully hereinafter. The rear body portion B111b of the shank B111 is, ofcourse, of suitable length, depending upon the desired overall length ofthe finished screw that is to be produced from the blank B110 inaccordance with the present method.

Referring now to FIG. 11, the modified form of the screw 111) thereillustrated and embodying the features of the present invention isessentially of the same construction as the screw 10, except in thiscase the thread 114 provided on both the front pilot end portion 111a ofthe shank 111 and on the rear body portion 111b of the shank 111comprises the previously described cyclically variable form. Asillustrated, the helical turns 114::1, 114b1, 11401 and 114:11 arecarried on the front pilot end portion 111a, while the helical turns1141111, 114x1, 114 1, 114z1, 114w2, etc., are carried upon the rearbody portion 1111b.

This cyclically variable form of the thread 114 may be viewed as aperturbation superimposed thereupon; whereby the major radius of thefront helical turns 114111, 114b1, etc., is constantly increasingprogressively rearwardly along the front pilot end portion 1110, but isalso subject to the previously described perturbation, wherein the valuethereof is cyclically variable with each complete cycle subtending theangle of 480, as previously explained, wherein A=360+B, and wherein3:120"; and whereby the major radius of the rear helical turns 1141-111,114x1, etc., is constant rearwardly along the rear body portion 111b,but is subject to the aforesaid perturbation, wherein the value thereofis cyclically variable with each complete cycle subtending the angle of480, as previously explained, wherein A=360+B, and wherein B=l. Also, inthe form of the thread 114 on the front pilot end portion 111a, theangular rate of increase of the major radius from turn to turnrearwardly therealong is substantially greater than the angular rate ofvariation of the aforesaid perturbation, so that there is an increase inthe major radius of the thread 114 between any two contiguous elementsof any turn thereof, on the front pilot end portion 111a in thedirection of the helix toward the rear body portion 1111:. Thisarrangement insures that an increasing major radius of the thread 114 onthe front pilot end portion 111a is presented to each element of thecylindrical surface of the bore in the workpiece, as the screw 116] isset therein.

The operation of the screw 11!) with respect to the asso ciatedworkpiece is essentially the same as that previously described inconnection with the screw 10, except that in this case, the thread isswaged in the bore formed in the workpiece fundamentally by the fronthelical turns 114411, 114b1,etc., incident to setting of the screw 11%,as is obvious from an inspection of the screw 110 in FIG. 11.

- Of course, the screw 110 may beproduced from the blank B110 employinga rolling step in the manner previously described in connection with theproduction of the screw 10, except in this case the dies employed mustbe constructed so as to efiect the particular form of the thread 114, asdescribed above.

Referring now to FIG. 12, the modified form of the screw 210 thereillustrated and embodying the features of the present invention isessentially of the same construction as the screws 10 and 110, except inthis case only the thread 214 provided on the front pilot end portion211a of the shank 211 comprises the previously described cyclicallyvariable form, the threadv 214 provided on the rear body portion 211!)of the shank 211 being of conventional form; As illustrated, the helicalturns 21 -1e11, 214b1, 214c1, 214111 and 214a2 are carried on the frontpilot end portion 211a, while the helical turns 214w, 214x, etc., arecarried upon the rear body portion 211]).

The major radius of the front helical turns 214a1, 214])1, etc., isconstantly increasing progressively rearwardly along the front pilot endportion 211a, and further comprise the previously describedperturbation, wherein the value thereof is cyclically variable with eachcomplete cycle subtending 480, as previously explained, wherein A=360+B,and wherein B 120. Of course, the minor radius of the front helicalturns 214a1, 214])1, etc., merely increases progressively rearwardlyalong the front pilot end portion 211a. The major radius and the minorradius of the rear helical turns 214w, 214x, etc., are fixed along therear body portion 211b, and are thus subject to no variation whatsoever.Moreover, the'major radius and the minor radius of the rear helicalturns 214w, 214x, etc., are as great as the respective maximum majorradius and maximum minor radius of the rearmost front helical turn214112, so that substantially all of the swaging action of the screw 210is performed by the thread 214 on the front pilot end portion 211a, andso'that the thread 214 on the rear body portion 211b then tightlyengages the thus formed thread produced in the associated workpiece,incident to the setting of the screw 210 in the associated workpiece.Accordingly, the operation of the screw 210 is essentially the same asthat of the screws 10 and 110, as previously described.

Of course, the screw 210 may be produced from the blank B110 employing arolling step in the manner previously described in connection with theproduction of the screw 10, except in this case, the dies employed mustbe constructed so as to elfect the particular form of the thread 214, asdescribed above. 7

Recapitulating: in the screw 10, the perturbation described is presentin only the portion of the thread 14 disposed on the rear body portion11b of the shank 11; in the screw 110, the perturbation described ispresent in both portions of the thread 114 respectively disposed on thefront pilot end portion 111a and on the rear body portion 111b of theshank 111; and in the screw 210, the perturbation described is presentin only the portion of the thread 214 disposed on the front pilot endportion 211a of the shank 211.

In view of the foregoing, it is apparent that there has been provided afluteless thread-forming tool, and specifically a fastening screw ofimproved construction and arrangement. This tool is Very advantageous,since the same is operative to form the internal thread in the genover,the improved tool is substantially easier to operate in itsthread-forming action than is a comparable conventional tool of thechip-forming type, in the sense that the improved tool requiressubstantially less driving torque than does the conventional toolmentioned.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A fluteless thread-forming tool for threading a generally cylindricalsurface; said tool comprising an elongated shank including a generallycylindrical rear body portion and a generally frusto-conicalforwardly-tapered front pilot end portion, and a continuous threadcarried on said-shank and including both a plurality of helical turns onsaid rear body portion and a plurality of helical turns onsaid frontpilot end portion, said thread having a fixed pitch, the turns on saidrear body portion having substantially the same minor radius andsuccessively forward ones of the turns on said front pilot end portionhaving generally reduced minor radii, the turns on at least one of saidshank portions having a crest projection from the root thereof that iscyclically variable between maximum and minimum values along the helixof said thread with a rotational angle A about the longitudinal axis ofsaid shank between adjacent thread positions of maximum crestprojection, wherein A=360+B, and wherein B is a fixed angle within theapproximate range 60 to 120.

2. The tool set forth in claim 1, wherein the fixed angle B is evenlydivisible into 360.

3. The tool set forth in claim 1, wherein B is approximately 120.

4. The tool set forth in claim 1, wherein B is approximately 90.

5. The tool set forth in claim 1, wherein B is approxi- V mately 72;

6. The tool set forth in claim 1, wherein B is approximately 60. t

7. A fiuteless thread-forming tool for threading a generally cylindricalsurface; said tool comprising an elongated shank including a generallycylindrical rear body portion and a generally frusto-conicalforwardly-tapered front pilot end portion, and a continuous threadcarried on said shank and including both a plurality of helical turns onsaid rear body portion and a plurality of helical turns on said frontpilot end portion, said thread having a fixed pitch, the turns on saidrear body portion having substantially the same minor radius andsuccessively forward ones of. the turns on said front pilot end portionhaving gradually reduced minor radii, the turns on said front pilot endportion having a crest projection from the root thereof that issubstantially fixed, the turns on said rear body portion having a crestprojection from the root thereof that is cyclically variable betweenmaximum and minimum values along the helix of said thread with arotational angle A about the longitudinal axis of said shank betweenadajcent thread positions of maximum crest projection, wherein A=360+B,wherein B is a fixed angle within the approximate range 60 to 120.

8. A fiuteless thread-forming tool for threading a generally cylindricalsurface; said tool comprising an elongated shank including a generallycylindrical rear body portion and a generally frusto-conicalforwardly-tapered front pilot end portion, and a continuous threadcarried on said shank and including both a plurality of helical turns onsaid rear body portion and a plurality of helical turns on said frontpilot end portion, said thread having cyclically variable betweenmaximum and minimum values along the helix of said thread with arotational angle A about the longitudinal axis of said shank betweenadjacent thread positions of maximum crest projection, wherein A=360+B,and wherein B is a fixed angle within the approximate range 60 to 9. Afluteless thread-forming tool for threading a generally cylindricalsurface; said tool comprising an elongated shank including a generallycylindrical rear body portion and a generally frusto-conicalforwardly-tapered front pilot end portion, and a continuous threadcarried on said shank and including both a plurality of helical turns onsaid rear body portion and a plurality of helical turns on said frontpilot end portion, said thread having a fixed pitch, the turns on saidrear body portion having substantially the same minor radius andsuccessively forward ones of the turns on said front pilot end portionhaving gradually reduced minor radii, the turns on said rear bodyportion having a crest projection from the root thereof that issubstantially fixed, the turns on said front pilot end portion having acrest projection from the root thereof that is cyclically variablebetwen maximum and minimum values along the helix of said thread with arotational angle A about the longitudinal axis of said shank betweenadjacent thread positions of maximum crest projection, wherein A=360+B,and wherein B is a fixed angle within the approximate range 60 to 120.

10. The tool set forth in claim 9, wherein the angular rate of increaseof the minor radius of successively rearward ones of the turns on saidfront pilot end portion is substantially greater than the angular rateof variation of the crest projection from the root thereof, so thatthere is an increase in the major radius of said thread between any twocontiguous elements of any turn thereof on said front pilot end portionin the direction toward said rear body portion. 7

11. A thread-swaging and fastening screw comprising an elongated shankincluding a generally cylindrical rear body portion and a generallyfrusto-conical forwardly tapered front pilot end portion, an enlargedhead carried on the rear end of said rear body portion, and a continuousthread carried on said shank and including both a plurality of helicalturns on said rear body portion and a plurality of helical turns on saidfront pilot end portion, said thread having a fixed pitch, the turns onsaid rear body portion having substantially the same minor radius andsuccessively forward ones of the turns on said front pilot end portionhaving gradually reduced minor radii, the turns on at least one of saidshank portions having a crest projection from the root thereof that iscyclically variable between maximum and minimum values along the helixof said thread with a rotational angle A aboutv the longitudinal axis ofsaid shank between adjacent thread positions of maximum crestprojection, wherein A=360+B, and wherein B is a fixed angle within theapproximate range 60 to 120.

12. A thread-swaging and fastening screw comprising an elongated shankincluding a generally cylindrical rear body portion and a generallyfrusto-conical forwardly tapered front pilot end portion, an enlargedhead carried on the rear end of said rear body portion, and a continuousthread carried on said shank and including both a plurality of helicalturns on said rear body portion and a plurality of helical turns on saidfront pilot end portion, said thread having a fixed pitch, the turns onsaid rear body portion having substantially the same minor radius andsuccessively forward ones of the turns on said front pilot end portionhaving gradually reduced minor radii, the turns on said rear bodyportion having a crest projection from the root thereof that issubstantially fixed, the turns on said front pilot end portion having acrest projection from the root thereof that is cyclically variablebetween maximum and minimum values along the helix of said thread with arotational angle A about the longitudinal axis of said shank betweenadjacent thread positions of maximum crest projection, wherein A=360+B,and wherein B is a fixed angle within the approximate range 60 to 120.

13. A thread-swaging and fastening screw comprising an elongated shankincluding a generally cylindrical rear body portion and a generallyfrusto-conical forwardly tapered front pilot end portion, an enlargedhead carried on the rear end of said rear body portion, and a continuousrolled thread carried on said shank and including both a plurality ofhelical turns on said rear body portion and a plurality of helical turnson said front pilot end portion, said thread having a fixed pitch, theturns on said rear body portion having substantially the same minorradius and successively forward ones of the turns on said front pilotend portion having gradually reduced minor radii, the turns on said rearbody portion having a crest projection from the root thereof that issubstantially fixed, the turns on said front pilot end portion having acrest projection from the root thereof that is cyclically variablebetween maximum and minimum values along the helix of said thread with arotational angle A about the longitudinal axis of said shank betweenadjacent thread positions of maximum crest projection, wherein A=360+B,and wherein B is a fixed angle within the approximate range 60 to 120.

Reterences fiited by the Examiner UNITED STATES PATENTS Re. 24,572 12/58Welles 10-152 2,352,982 7/44 Tomalis 85-48 FOREIGN PATENTS 1,265,9995/61 France.

316,627 8/29 Great Britain.

EDWARD C. ALLEN, Primary Examiner.

1. A FLUTELESS THREAD-FORMING TOOL FOR THREADING A GENERALLY CYLINDRICALSURFACE; SAID TOOL COMPRISING AN ELONGATED SHANK INCLUDING A GENERALLYCYLINDRICAL REAR BODY PORTION AND A GENERALLY FRUSTO-CONICALFORWARDLY-TAPERED FRONT PILOT END PORTION, AND A CONTINUOUS THREADCARRIED ON SAID SHANK AND INCLUDING BOTH A PLURALITY OF HELICAL TURNS ONSAID REAR BODY PORTION AND A PLURALITY OF HELICAL TURNS ON SAID FRONTPILOT END PORTION, SAID THREAD HAVING A FIXED PITCH, THE TURNS ON SAIDREAR BODY PORTION HAVING SUBSTANTIALLY THE SAME MINOR RADIUS ANDSUCCESSIVELY FORWARD ONES OF THE TURNS ON SAID FRONT PILOT ENDS PORTIONHAVING GENERALLY REDUCED MINOR RADII, THE TURNS ON AT LEAST ONE OF SAIDSHANK PORTIONS HAVING A CREST PROJECTION FRON THE ROOT THEREOF THAT ISCYLICIALLY VARIABLE BETWEEN MAXIMUM AND MINIMUM VALUES ALONG THE HELIXOF SAID THREAD WITH A ROTATIONAL ANGLE A ABOUT THE LONGITUDINAL AXIS OFSAID SHANK BETWEEN ADJACENT THREAD POSITIONS OF MAXIMUM CRESTPROJECTION, WHEREIN A=360.+B, AND WHEREIN B IS A FIXED ANGLE WITHIN THEAPPROXIMATE RANGE
 60. TO 120..